Fixes missing prompt template or system template (#2408)

* Fix issue #2402: Handle missing templates gracefully

Co-Authored-By: Joe Moura <joao@crewai.com>

* Fix import sorting in test files

Co-Authored-By: Joe Moura <joao@crewai.com>

* Bluit in top of devin-ai integration

* Fixed test cases

* Fixed test cases

* fixed linting issue

* Added docs

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Joe Moura <joao@crewai.com>

tests/agent_test.py

@@ -72,9 +72,54 @@ def test_agent_creation():
     assert agent.role == "test role"
     assert agent.goal == "test goal"
     assert agent.backstory == "test backstory"
-    assert agent.tools == []
+
+def test_agent_with_only_system_template():
+    """Test that an agent with only system_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        system_template="You are a test agent...",
+        # prompt_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
+
+def test_agent_with_only_prompt_template():
+    """Test that an agent with only system_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        prompt_template="You are a test agent...",
+        # prompt_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
 
 
+def test_agent_with_missing_response_template():
+    """Test that an agent with system_template and prompt_template but no response_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        system_template="You are a test agent...",
+        prompt_template="This is a test prompt...",
+        # response_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
+    
 def test_agent_default_values():
     agent = Agent(role="test role", goal="test goal", backstory="test backstory")
     assert agent.llm.model == "gpt-4o-mini"